Cosgrove D J
Department of Biology, Pennsylvania State University, University Park, USA.
Gravit Space Biol Bull. 1998 May;11(2):61-70.
Gravity responses in plants often involve spatial and temporal changes in cell growth, which is regulated primarily by controlling the ability of the cell wall to extend. The wall is thought to be a cellulose-hemicellulose network embedded in a hydrated matrix of complex polysaccharides and a small amount of structural protein. The wall extends by a form of polymer creep, which is mediated by expansins, a novel group of wall-loosening proteins. Expansins were discovered during a molecular dissection of the "acid growth" behavior of cell walls. Expansin alters the rheology of plant walls in profound ways, yet its molecular mechanism of action is still uncertain. It lacks detectable hydrolytic activity against the major components of the wall, but it is able to disrupt noncovalent adhesion between wall polysaccharides. The discovery of a second family of expansins (beta-expansins) sheds light on the biological role of a major group of pollen allergens and implies that expansins have evolved for diverse developmental functions. Finally, the contribution of other processes to wall extensibility is briefly summarized.
植物中的重力反应通常涉及细胞生长的空间和时间变化，这主要通过控制细胞壁的伸展能力来调节。细胞壁被认为是一个嵌入复杂多糖水合基质和少量结构蛋白中的纤维素 - 半纤维素网络。细胞壁通过一种聚合物蠕变的形式伸展，这是由扩张蛋白介导的，扩张蛋白是一组新型的细胞壁松弛蛋白。扩张蛋白是在对细胞壁“酸生长”行为进行分子剖析的过程中发现的。扩张蛋白以深刻的方式改变植物细胞壁的流变学，但其分子作用机制仍不确定。它对细胞壁的主要成分缺乏可检测到的水解活性，但它能够破坏细胞壁多糖之间的非共价粘附。第二类扩张蛋白（β - 扩张蛋白）的发现揭示了一大类花粉过敏原在生物学上的作用，并表明扩张蛋白已经进化以实现多种发育功能。最后，简要总结了其他过程对细胞壁伸展性的贡献。
